1. Field of the Invention
The invention relates to a method of finding a maximum power point of a photovoltaic generator.
Photovoltaic generators have characteristic power curves generally including a maximum power operating point. A certain generator current and a certain generator voltage are associated with this operating point.
Methods are known, by which the generator load, e.g., the generator current, is set so that the photovoltaic generator is operated at maximum power.
Such type methods are referred to as Maximum Power Point Tracking (MPPT).
2. Description of the Prior Art
A method presented in DE 199 04 561 C1 consists in utilizing an additional sensor that measures the incoming radiation and sets a maximum power through a characteristic curve measuring circuit and a microcomputer. If a shadow falls onto the sensor or if part of the generator is shadowed, an operating point is created that will not supply maximum power, this causing the energy efficiency of the system as a whole to drop.
Another method is known from DE 199 09 609 C1. Herein, no sensor is utilized but the generator's characteristic curve is measured directly by making use of a capacitor. A microcomputer serves to set the optimal operating point acquired. If however a generator part is shadowed, a plurality of local power maxima, which may have different heights, can occur. Therefore, it may happen that the power output by a partially shadowed generator will not be at its maximum and that part of the solar energy will not be used.
Another method for setting the maximum power point of a solar generator in a photovoltaic array is described in DE 100 60 108 A1. The peak of maximum power is set by measuring the physical parameters of the generator once as long as it is not partially shadowed.
The document DE 4325436 C2 describes a method by which the generator is periodically short-circuited and unloaded. The disadvantage of this method also is that partial shadowing is not recognized.